Abstract: The proposed field trial, motivated by a major epidemiological study on urinary stone disease, will investigate whether or not soft drink consumption can cause urinary stone disease. The established and confirmed epidemiological link may or may not be causal. This randomized trial of 1100 recent male stone victims, who consumed at least 300 ml per day of soft drinks during the prior six months, is necessary to answer this causality question. The potential economic and human impact of this proposed study fully justify its conduct. The soft drink industry stands to lose at least $75,000,000 in profits per year if cause-effect is established. It is further estimated that over 7,000 recurrences per year could be spared, if causality is demonstrated. The study will be fairly easy to complete. Patients will be obtained through participating Urologists, yet to be selected. Randomization (balanced for prior stone history, Urologist, and prior soda consumption) will place subjects into one of two groups: Experimental (advised to abstain from soda) or Control (no advice given). In order to minimize dropouts, rigorous follow-up methods will be employed. Only data relevant to the study questions will be collected. Participants will need only to fill out an eight item questionnaire, once every six months, to comply with data requirements. The collection of ancillary data would significantly add to the cost of this project, while at the same time, reduce subject compliance to data submission. Therefore, this proposal focuses directly on the study question, but does address issues beyond the main objectives.